1. Field of the Invention
The present invention relates to a data communication apparatus for setting a transmission bit rate in accordance with line quality.
2. Related Background Art
In a prior art apparatus of this type, for example, in a facsimile apparatus, a TCF signal (training check signal) is received by a modem at a maximum transmission bit rate and a control unit of the facsimile apparatus determines whether the received TCF signal has been properly received or not. If the TCF signal has been properly received, it sends a CFR (confirmation to receive) signal to inform to the sending station that it is capable of receiving the image communication at that transmission bit rate and thereafter it conducts the image transmission at that transmission bit rate. If the TCF signal has not been properly received, it sends a FTT (failure to train) signal to inform to the sending station that it cannot conduct the image transmission at that transmission bit rate. When the sending station receives the FTT signal, it sets the transmission bit rate of the modem one step lower and resends the TCF signal. In this manner, the control unit of the facsimile apparatus sets the transmission bit rate of the modem to the transmission bit rate at which the TCF signal can be properly received.
The modem which complies with the V.34 recommendation has a function in the modem itself to set a transmission baud rate and a transmission bit rate by line proving, long training and parameter exchange with a modem of a destination station.
However, since the setting of the transmission baud rate and the transmission bit rate between the modems is conducted with the modem of the destination station by the function of its own modem separately from the actual image data communication, it may happen that it does not always correspond to the actual communication status of the image data.
As a result, when the transmission baud rate and the transmission bit rate established between modems do not correspond to the actual image data, many communication errors of the image data take place or a lower baud rate or bit rate may be set in spite of the fact that the image communication at a higher rate is attainable.